1. Field of the Invention
This invention relates to a travel assembly, which is to be arranged on a wheeled working vehicle such as a dump truck for transporting, for example, crushed rocks dug in a mine or the like, and has a travel motor and a planetary gear reduction mechanism for transmitting rotation of a rotary shaft of the travel motor to a wheel at a reduced speed.
2. Description of the Related Art
In general, drive assemblies for driving drive wheels of a wheeled working vehicle, for example, a dump truck to travel are each provided with a cylindrical spindle to be mounted on a vehicle body, a rotary shaft arranged extending in an axial direction through the spindle and rotationally drivable by a driving source such as an electric motor, a rim rotatably arranged on an outer periphery of a free end portion of the spindle via a bearing to permit mounting of a wheel on the rim, and a multiple-stage, planetary gear reduction mechanism for transmitting rotation of the rotary shaft to the rim at a reduced speed.
The planetary gear reduction mechanism transmits a rotation output from the driving source composed, for example, of the electric motor to the wheel via the rim at a reduced speed, so that a rotary torque is produced at the drive wheel of the vehicle, such as a front wheel or rear wheel, to cause the dump truck to travel.
In a conventional technology disclosed in U.S. Patent Application Publication No. 2004/0065169 A1, two sets of planetary gear reduction mechanisms are included for increasing rotary torque in a vehicle and composed of a sun gear, plural planet gears, a ring gear, a carrier, and the like, respectively. Each planetary gear reduction mechanism is constructed such that the carrier rotatably supports the plural planet gears, which are rotatable in accordance with rotation of the sun gear, via plural support pins and rotation of the respective planet gears are transmitted to the ring gear and are outputted as a rotation output to an outside. On the other hand, the rotary shaft is rotatably supported by a bearing arranged at an intermediate location in a longitudinal direction from a motor to the planetary gear reduction mechanism.
In the conventional technology disclosed in the above-mentioned U.S. Patent Application Publication No. 2004/0065169 A1, however, large rotational loads are applied to each travel assembly in such a dump truck, and therefore, it is necessary to feed lube oil to the rotary shaft and bearing to maintain them under lubrication.
In the above-described construction, however, holding of a great deal of lube oil within the travel assembly results in energy loss and heat production due to resistance to agitation of the lube oil as a result of rotation of the respective gears. It is, therefore, common to set the quantity of lube oil, which is to be held within the travel assembly, at a minimum need (for example, approximately from ⅕ to ⅓ of the internal capacity). When set so, the oil level is located on a side lower than the rotary shaft so that only the planet gears and the carrier supporting the planet gears thereon are immersed in the lube oil and the rotary shaft and its bearing remain free from immersion in the lube oil.
In the conventional technology disclosed in U.S. Patent Application Publication No. 2004/0065169 A1, the bearing that rotatably supports the rotary shaft thereon is arranged in proximity to the planet gears in expectation of lubrication with lube oil mist splashed as a result of rotation of the planet gears.
The conventional technology disclosed in U.S. Patent Application Publication No. 2004/0065169 A1, however, involves a potential problem that the lube oil may not be fed in any sufficient quantity to the bearing for the rotary shaft because the lube oil for lubricating the bearing, which rotatably supports the rotary shaft thereon, is fed only by a method that relies upon dispersion of lube oil mist as a result of splashing of the lube oil by rotation of the planet gears. A failure to feed the lube oil in a sufficient quantity is accompanied by a problem that the bearing is reduced in durability and service life.